The present invention relates to an automatic white balance adjusting circuit for automatically adjusting a white balance in a television receiver or a monitor apparatus.
In a television receiver or a monitor apparatus, when a white color reference signal is inputted, a predetermined color temperature must be reproduced at a cathode-ray tube (hereinafter, referred to as CRT). In general, the rate of each of output lights R (red), G (green), and B (blue) of the CRT is determined depending on the rate of each cathode current. However, characteristics of the cathode current to a cathode voltage differs with the CRT. Therefore, in order to reproduce a predetermined color temperature, it is required to adjust the rate of the cathode current among R, G, and B, by the CRT.
Conventionally, the CRT screen has been monitored on a television camera or the like to detect a white balance state, the detected value has been fed back to a computer system or service personnel for process adjustment to compare it with a predetermined reference value, and the DC voltage level and gain of each of the outputs R, G, and B has been adjusted according to the comparison results. In addition, during this adjustment, variable resistors provided at a DC voltage level adjusting circuit and a gain adjusting circuit has been manually adjusted or adjustment data stored in a storage circuit has been rewritten through a data bus.
However, in the above mentioned conventional method, an industrial television camera, a computer system for process adjustment, or service personnel is required at an adjustment site. Therefore, there is a problem that the white balance characteristics cannot be self-adjusted following an change of CRT with an elapse of time after shipment of the television receiver or monitor apparatus.
In recent years, an Automatic Kine Bias (AKB) circuit for automatically perform such adjustment is available in use. In this circuit, a reference signal is inputted during a vertical blanking period of a video signal, a cathode current of the CRT at this time is detected, and a white balance is automatically adjusted using the detected value.
FIG. 1 shows an example of a conventional circuit of such AKB circuit. A while balance is adjusted by setting a drive gain (AC amplitude) and a cutoff level (DC voltage level) on each of the R, G, and B axes. Specifically, during a certain period, the cutoff level is adjusted using a reference signal 1 (black level) substituted for a video signal, and similarly, during a period free of being superimposed on the reference signal 1, the drive gain is adjusted using a reference signal 2 (white level) substituted for the video signal. These two black and white levels are adjusted, thereby equally setting a ratio of the respective input signal and cathode current of each of the R, G, and B axes.
Now, the AKB circuit of FIG. 1 will be specifically described.
Switch circuits 1, 2, 3 each select and output respective one among R, G, and B signals and the reference signal 1 (black level) and the reference signal 2 (white level). A period for selecting the reference signals 1 and 2 is a period that is a vertical blanking period, but is not a vertical feedback period, i.e., a part of a period that is generally over-scanned and not visualized by a user. The level of the reference signal 1 corresponding to a reference black level is about 3 to 5 IRE, for example (a peak of the white signal is 100IRE), and the level of the reference signal 2 corresponding to a reference white level is about 30 to 50 IRE, for example.
In addition, the above R, G, and B signals are primary color signals of each of the R, G, and B axes in a three-primary color drive, and the brightness, tint or the like of these primary signals are controlled in advance.
Drive gain adjusting circuits 4, 5, and 6 respectively consisting of gain control amplifiers perform adjustment of drive gain to signals outputted respectively from switch circuits 1, 2, and 3, i.e., adjustment of an AC amplitude. In addition, cutoff adjusting circuits 7, 8, 9 respectively consisting of clamp circuits, for example, performs adjustment (for example, clamping) of the DC level of signals output respectively from the drive gain adjusting circuits 4, 5, and 6. Outputs of the cutoff adjusting circuits 7, 8, and 9 are supplied to bases of output transistors (PNP transistors) 13, 14, and 15 each via respective one of drive circuits 10, 11, and 12. Emitters of these transistors 13, 14, and 15 are connected respectively to the cathode electrodes of the R, G, and B axes of the CRT 16. These transistors 13, 14, and 15 are driven by outputs from the drive circuits 10, 11, and 12, whereby a current flow the cathode electrode of each of the R, G, and B axes of CRT 16, and CRT 16 are driven to be displayed.
To collectors of the above transistors 13, 14, and 15 each, resistors 17, 18, and 19 for converting the current flowing through each cathode electrode into a voltage are connected. Drop voltages in these resistors 17, 18, and 19 are sampled respectively at a sample hold circuit (S/H) 20, 21 and 22. These sample hold circuits 20, 21, and 22 samples voltages proportional to a cathode current during a certain period, for example 1H (1 horizontal period). The sampled voltages are held by capacitors 23, 24, and 25 for holding a black level respectively and by capacitors 26, 27, and 28 for holding a white level.
The voltages held by the above capacitors 23, 24, and 25 are compared respectively with a reference voltage corresponding to the reference black level in comparator circuits 29, 30, and 31. The reference voltage is outputted from a reference voltage source 32. The comparison results of these comparator circuits 29, 30, and 31 are supplied respectively to the cutoff adjusting circuits 7, 8, and 9, and the DC level is adjusted by each of the R, G, and B axes.
The voltages held by the above capacitors 26, 27, and 28 are compared respectively with a reference voltage corresponding to the reference white level in the comparator circuits 33, 34 and 35. The reference voltage is outputted from a reference voltage source 36. The comparison results of these comparator circuits 33, 34, and 35 are supplied respectively to drive gain adjusting circuits 4, 5, and 6, and the AC amplitude is adjusted by each of the R, G, and B axes.
In the AKB circuit shown in FIG. 1, by each of the R, G, and B axes, adjusting operation of an AC amplitude and an adjusting operation of a DC level are controlled respectively by each negative feedback loop consisting of drive gain adjusting circuits 4, 5 and 6; cutoff adjusting circuits 7, 8 and 9; drive circuits 10, 11, and 12; transistors 13, 14, and 15; sample hold circuits 20, 21, and 22; and comparator circuits 29 to 35. At a time when voltages of both input terminals of each of comparator circuits 29 to 31 and 33 to 35 are equal to each other, the above operation of each negative feedback loop becomes stable. At a time when operation of each feedback loop becomes stable, a rate of the cathode current among each of the R, G, and B axes to a reference signal is set to be equal.
In the meantime, in the conventional AKB circuit shown in FIG. 1, in order to hold a voltage obtained by converting a cathode current during a keyline period, sample hold circuits 20 to 22 require capacitors 23 to 28. Since this keyline period is b 1V (1 vertical period, about 17 mS), these capacitors require a relatively large capacitance, and use about several xcexcF to 10 xcexcF.
As a result, an integrated AKB circuit can not incorporate these capacitors in an integrated circuit, and is required to be provided outside of the integrated circuit. In addition, the integrated circuit is required to provide a dedicated external terminal for providing these capacitors outside the circuit, and large sizing of the integrated circuit is unavoidable.
In the meantime, in the CRT, even if a cathode voltage is not supplied, and the display screen is placed in a completely black state, a leak current may flow a cathode electrode. Therefore, at this time, a voltage to be obtained by converting the cathode current is not 0V, and the voltage with this leak current is added to hold voltages of capacitors 23 to 28 of the sample hold circuits 20 to 22.
FIG. 2 is an extracted circuit diagram showing a resistor 17 for detecting a cathode current in R axis and converting the detected current into a voltage and a comparator circuit 29 for comparing the converted voltage by the resistor 17 with a reference voltage corresponding to a reference black level.
During reference signal input, a leak current I leak flows a cathode electrode in addition to a cathode current Ik corresponding to this reference signal. Therefore, a drop voltage of, VIk=Rxc3x97(Ik+I leak) (R is a resistance value of resistor 17) is generated at a resistor 17 for current detection.
That is, a drop voltage with a leak current is generated at the resistor 17, and thus, an optimal cutoff or drive gain cannot be sometimes obtained.
In addition, if a value of a leak current differs among three axes, R, G, and B, there occurs a problem that a correct white balance cannot be obtained.
As a measure for solving such problem that a white balance is displaced due to a leak current, a circuit as shown in FIG. 3 is designed conventionally. For this circuit, a clamp circuit 41 for clamping a cathode current Ik during a vertical blanking period is added to the circuit shown in FIG. 2.
This clamp circuit 41 is composed of a clamping capacitor 42, a clamping voltage source 43, and a switch circuit (SW) 44.
In this circuit, where a leak current exists in a cathode electrode, a drop voltage corresponding to this current is generated between both ends of the resistor 17 during vertical blanking period. In addition, the switch circuit 44 is turned. ON during a period of a vertical blanking period, and a voltage of connection node N1 between the comparator circuit 29 and the capacitor 42 is set to be substantially equal to that of the clamping voltage source 43.
On the other hand, another period of the vertical blanking period, the drop voltage corresponding to a current in addition between a current corresponding to the reference signal and the leak current is generated between both ends of the resistor 17. At this time, the switch circuit 44 is turned OFF, and a drop voltage due to a current corresponding to only the reference signal is generated at connection node N1 between the comparator circuit 29 and a capacitor 42. That is, a voltage due to a leak current component is offset. Then, this voltage of node N1 is compared with a reference voltage of the reference voltage source 32 by means of the comparator circuit 29.
However, in the circuit of FIG. 3, a clamping capacitor 42 is further required.
In this manner, in the conventional AKB circuit, there is a need for providing a number of capacitor having its large capacitance. As a result, a number of parts are required to be externally provided, and thus, there is a disadvantage that manufacturing cost during integrated circuiting becomes high.
In addition, in the conventional AKB circuit, there is a disadvantage that an optimal cutoff or drive gain cannot be obtained by the influence of a leak current flowing through a cathode electrode. Further, there occurs a problem that many more capacitors are required to eliminate the influence of this leak current.
It is a first object of the present invention to provide an automatic white balance adjusting circuit capable of eliminating the influence of a leak current of a cathode using a smaller number of capacitors and optimally adjusting cutoff or drive gain.
It is a second object of the present invention to provide an automatic white balance adjusting circuit capable of being inexpensively manufactured without requiring an external capacitor during integration.
It is a third object of the present invention to provide an automatic white balance adjusting circuit capable of, even if a DC level of a video signal has changed rapidly by variation of a high voltage supplied to a cathode-ray tube, returning variation of this DC level to an original value rapidly, and then, maintaining it to a certain value.
It is a fourth object of the present invention to provide an automatic white balance adjusting circuit capable of, even if discrete data is employed when a DC level of a video signal is adjusted using data, converging the DC level at one point.
According to the present invention, there is provided an automatic white balance adjusting circuit for automatically adjusting a white balance of a color image display tube having at least one cathode electrode comprises: a selector circuit for receiving a color video signal having a vertical blanking period and at least one reference signal, selecting the color video signal, and selecting and outputting the at least one reference signal during a partial period of the vertical blanking period; an adjusting circuit for receiving a signal outputted from the selector circuit, adjusting at least one of a DC level and an AC amplitude of the signal in accordance with a control signal, and outputting the signal thus adjusted; a drive circuit for receiving the output signal of the adjusting circuit and outputting a driving signal to be supplied to the at least one cathode electrode of the color image display tube according to the output signal; a detector circuit connected to the color image display tube and detecting a voltage according to a current flowing through the cathode electrode of the color image display tube; a first voltage hold circuit for receiving a voltage detected by the detector circuit and holding the voltage; an arithmetic circuit for receiving a voltage detected by the detector circuit during a period in which the reference signal is selected by the selector circuit and a voltage held by the first voltage hold circuit during a period in which neither of the color video signal and reference signal are selected, and obtaining a voltage in difference between these voltages; and a comparator circuit for, receiving a voltage in difference obtained by the arithmetic circuit, comparing the voltage in difference with a reference voltage, and generating the control signal to control an operation of the adjusting circuit according to the comparison result.
According to the present invention, there is provided an automatic white balance adjusting circuit for automatically adjusting a white balance of a color image display tube having at least one cathode electrode, comprises: a selector circuit for receiving a color video signal having a vertical blanking period and at least one reference signal, selecting the color video signal, and selecting and outputting the at least one reference signal during a partial period of the vertical blanking period; an adjusting circuit for receiving a signal outputted from the selector circuit, adjusting at least one of a DC level and an AC amplitude of the signal in accordance with a control signal, and outputting the signal thus adjusted; a drive circuit for receiving the output signal of the adjusting circuit, and outputting a driving signal to be supplied to the at least one cathode electrode of the color image display tube according to the output signal; a detector circuit connected to the color image display tube and detecting a voltage according to a current flowing through the at least one cathode electrode of the color image display tube; a voltage hold circuit for receiving a voltage detected by the detector circuit during a period in which neither of the color video signal and the at least one reference signal are selected, and holding the voltage; a comparator circuit having a pair of input nodes, the voltage detected by the detector circuit being supplied to one input node during a period in which the at least one reference signal is selected by the selector circuit, a reference voltage being supplied to the other input node, the comparator circuit comparing these two voltages supplied to the pair of input nodes, and generating the control signal for controlling an operation of the adjusting circuit according to the comparison result; and a reference voltage generator circuit for generating the reference voltage, receiving a voltage held by the voltage hold circuit, and changing a value of the reference voltage according to the voltage.
According to the present invention, there is provided an automatic white balance adjusting circuit for automatically adjusting a white balance of a color image display tube having at least one cathode electrode, comprises: a selector circuit for receiving a color video signal having a vertical blanking period and at least one reference signal, selecting the color video signal, and selecting and outputting the at least one reference signal during a partial period of the vertical blanking period; an adjusting circuit for receiving a signal outputted from the selector circuit, adjusting at least one of a DC level and an AC amplitude of the signal in accordance with a control signal, and outputting the signal thus adjusted; a drive circuit for receiving the output signal of the adjusting circuit and outputting a driving signal to be supplied to the at least one cathode electrode of the color image display tube according to the output signal; a first detector circuit connected to the color image display tube and detecting a voltage according to a current flowing through the cathode electrode of the color image display tube; a first comparator circuit for receiving a voltage detected by the first detector circuit during a period in which the at least one reference signal is selected by the selector circuit, and comparing the voltage with a first reference voltage; a memory circuit for storing data for controlling an operation of the adjusting circuit; an update circuit for receiving the comparison result of the first comparator circuit and data stored in the memory circuit, updating the data based on the comparison result of the first comparator circuit, and supplying the updated data to the memory circuit, the updated data being stored again in the memory circuit; and a D/A converter for receiving data stored in the memory circuit, converting the data into an analog signal, and output the converted signal to the adjusting circuit as the control signal.
According to the present invention, there is provided an image display apparatus comprises: an adjusting circuit for adjusting a DC level and an AC amplitude of a color image signal and outputting the color image signal thus adjusted, the color image signal representing even-numbered field and odd-numbered field alternately repeated, each field having a vertical blanking period; a color image display tube to be applied with a high voltage, having at least one cathode electrode; a drive circuit for receiving an output signal of the adjusting circuit and outputting a drive signal to the cathode electrode of the color image display tube in accordance with the output signal; a high-voltage fluctuation detecting circuit for detecting fluctuation of the high voltage applied to the color image display tube; and a control circuit for controlling the adjusting circuit, causing the adjusting circuit to adjust the DC level preferentially when the fluctuation of the high voltage is detected by the high-voltage fluctuation detecting circuit and causing the adjusting circuit to adjust the DC level and the AC amplitude alternately for any adjacent two fields which are an even-numbered one and odd-numbered one when the fluctuation of the high voltage is not detected by the high-voltage fluctuation detecting circuit.
According to the present invention, there is provided an image display apparatus comprises: a control voltage generator circuit for generating a control voltage such that a predetermined cathode current flows through a cathode electrode of an image display tube during an adjustment period of at least one of a DC level and an AC amplitude of a video signal; a data change circuit for receiving the control voltage, and changing data in a direction in which a value of an analog voltage obtained by analog-converting the data is close to the control voltage; and a detector circuit for receiving the control voltage and analog voltage, and detecting data in which an absolute value indicative of a difference between the analog voltage obtained by analog-converting data before and after the,change and the control voltage is smaller, wherein the at least one of a DC level and an AC amplitude of the video signal is adjusted by using an analog voltage obtained by analog-converting the detected data as data whose absolute value indicative of a difference between the analog data and the control voltage is smaller in the detector circuit.
According to the present invention, there is provided an image display apparatus comprises: a first detector circuit for updating data during an adjustment period of at least one of a DC level and an AC amplitude of a video signal, and detecting cathode currents flowing through a cathode electrode of an image display tube before and after the update, respectively; and a second detector circuit for receiving the detected result of the first detector circuit, and detecting data in which an absolute value indicative of a difference between a value of the cathode current detected and a predetermined reference value is smaller, wherein the at least one of a DC level and an AC amplitude of a video signal is adjusted by using an analog voltage obtained by analog-converting the detected data in the second detector circuit.
According to the present invention, there is provided an image display apparatus comprises: a detector circuit for changing data during an adjustment period of at least one of a DC level and an AC amplitude of a video signal, and detecting cathode currents flowing through a cathode electrode of an image display tube before and after the change; a judging circuit for receiving the detected result of the detector circuit, and when values of the detected cathode currents change across a predetermined convergence value, judging that the data has converged; and a data fixing circuit for receiving the judgment result of the judging circuit, and when convergence of the data is judged, fixing to data corresponding to any of a time when a value of the cathode current changes across the convergence value or a time before a value of the cathode current changes across the convergence value, wherein the at least one of a DC level and an AC amplitude of a video signal is adjusted by using the fixed data.
Additional objects and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and obtained by means of the instrumentalities and combinations particularly pointed out hereinafter.